1. Field of the Invention
This invention relates to a calorimetric absorbance measurement apparatus used in a biochemical analyzer.
2. Description of the Prior Art
Measurement of cholesterol levels or other biochemical data using such samples as blood plasma, serum or urine is carried out by using a biochemical analyzer, for example. Generally, this sort of measurement is performed by injecting a sample held in a sample tube and a reagent held in a reagent bottle into a cuvette which is formed of heat-resistant hard glass placed in a reaction vessel to cause a reaction therein, and measuring the absorbance of a reaction fluid to determine the cholesterol level, for instance, from obtained data.
A colorimetric absorbance measurement method is commonly used for measuring the absorbance. In this measurement method, a light source like an incandescent lamp emits light containing multiple wavelengths, a filter passes only such light components that have wavelengths falling within a range centering on a specific wavelength suited to an intended test item, and the light of the specific range of wavelength is passed through the reaction fluid in the cuvette to measure its absorbance. The filter commonly used in the colorimetric absorbance measurement method for taking out the desired wavelengths is a glass filter or an interference filter placed in a light path, for instance. An alternative to this filtering method that has also been commonly used is a grating method which disperses light from a light source into its wavelength components by use of a diffraction grating, for example.
Since the grating method is relatively expensive and makes it difficult to reduce equipment size due to the use of the diffraction grating, for instance, the filtering method has conventionally been used more often than the grating method in small-sized analyzers.
Since the colorimetric absorbance measurement utilizes different wavelengths depending on test items as stated above, it is essential to successively take out wavelengths of several ranges when conducting multiple tests. Whereas the diffraction grating used in the grating method selectively takes out wavelengths of several ranges at the same time, each filter used in the filtering method can take out wavelengths of one range only. Therefore, it is necessary to prepare multiple filters suitable for intended test items when using the filtering method.
As an example of a prior art arrangement, Japanese Laid-open Patent Publication No. 8-68788 discloses an apparatus for automatically measuring the quality, color and turbidity of tap water using the filtering method for calorimetric absorbance measurement, although this apparatus is not used as a biochemical analyzer for measuring samples in multiple cuvettes while sequentially moving them to the optical axis of a measuring light beam. The apparatus of the disclosure is constructed such that light emitted from a light source is passed through a cell containing water to be tested and a filter which transmits light components of wavelengths falling within a range centering on a specific wavelength, and the light components which have passed through the cell and the filter are converted into an electric signal, from which measurement results are calculated and output. In this apparatus, a rotating disklike light-dispersing device provided with at least four filters capable of passing specific wavelengths is caused to rotate and halt in successive steps, and a measurement is made when each filter has come to a halt.
The apparatus disclosed in the aforementioned Patent Publication controllably rotates the disklike light-dispersing device in such a way that the filter suited to the test item is placed in the light path and a measurement of the absorbance is performed when the light-dispersing device is at a halt. This approach, however, has a problem that a relatively long period of time is required for each measurement because the measurement should be made after each filter of the disklike light-dispersing device has been completely halted. More specifically, this approach requires a long measurement time overall and the number of wavelengths at which calorimetric absorbance measurements are performed for individual reaction fluids decreases. If the measurement is carried out before each filter of the disklike light-dispersing device is completely halted to achieve a high efficiency, the reliability of measurement data will deteriorate.